Tomoharu's younger sister, she is not initially a member of Partisan, but joins the fight to save Tokyo as well as protect her big brother. Aya is 19 years old. She can wield daggers, staves and guns.

After the destruction of Partisan's base, Naoki Takeuchi ends up in Shinjuku, where he meets Aya. He is injured heavily, but Aya finds him in a park and rescues him. She reveals she is related to Tomoharu, and decides to tag along with Naoki to ensure her brother is safe. After Naoki is reunited with Kaoru and Tomoharu, she becomes a permanent member of the party.

When the team ends up in the dystopic future of Slum Tokyo in 2024, Aya learns her brother has been brainwashed. With her newfound powers, which seem to originate from a paradise-like world named Amnesia, she is able to save her brother. Her new abilities consist of Dia, Ma- spells and Rimudora.